x86/xen: Make the secondary CPU idle tasks reliable

commit c3881eb58d56116c79ac4ee4f40fd15ead124c4b upstream.

The unwinder reports the secondary CPU idle tasks' stack on XEN PV as
unreliable, which affects at least live patching.
cpu_initialize_context() sets up the context of the CPU through
VCPUOP_initialise hypercall. After it is woken up, the idle task starts
in cpu_bringup_and_idle() function and its stack starts at the offset
right below pt_regs. The unwinder correctly detects the end of stack
there but it is confused by NULL return address in the last frame.

Introduce a wrapper in assembly, which just calls
cpu_bringup_and_idle(). The return address is thus pushed on the stack
and the wrapper contains the annotation hint for the unwinder regarding
the stack state.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Markus Boehme <markubo@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 64e6ec2c32a76640215c5a00cc93ff9fed8a425d..9d9777ded5f7bab8ed797c084ad6c5ce794a1156 100644 (file)
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -53,6 +53,7 @@ static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 };
 static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 };
 
 static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id);
+void asm_cpu_bringup_and_idle(void);
 
 static void cpu_bringup(void)
 {
@@ -310,7 +311,7 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
         * pointing just below where pt_regs would be if it were a normal
         * kernel entry.
         */
-       ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
+       ctxt->user_regs.eip = (unsigned long)asm_cpu_bringup_and_idle;
        ctxt->flags = VGCF_IN_KERNEL;
        ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
        ctxt->user_regs.ds = __USER_DS;

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index deb6abe5d346ca9992dc20bf366d535a29d21489..591544b4b85a2a4bc6aabd622cbc52bc2ed08ba3 100644 (file)
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -58,6 +58,16 @@ ENTRY(startup_xen)
        call xen_start_kernel
 END(startup_xen)
        __FINIT
+
+#ifdef CONFIG_XEN_PV_SMP
+.pushsection .text
+SYM_CODE_START(asm_cpu_bringup_and_idle)
+       UNWIND_HINT_EMPTY
+
+       call cpu_bringup_and_idle
+SYM_CODE_END(asm_cpu_bringup_and_idle)
+.popsection
+#endif
 #endif
 
 .pushsection .text